1. Field of the Invention
The present invention relates generally to television tuning systems and more particularly to all-electronic tuning systems which operate to recall a programmed sequence of channel numbers.
2. Description of the Prior Art
Early suggested digital television tuning systems employed various forms of information retention. As early as 1969 a paper by Doyle and Mills, BTR 15, No. 2, July 1969, showed a diagram with a shift register coupled to a push buttom panel feeding information to a comparator in a system using a frequency snythesizer tuning technique. The shift register operated as a temporary storage device for the process of relating the encoded information to a birdy or comb frequency.
U.S. Pat. No. 3,654,557 to Sakamoto and Ichinohe, dated Apr. 4, 1972, described a tuning system for selecting from among a limited number or preselected channels having a maximum capacity of 12 VHF and 4 UHF television channels. Binary switching is used to activate an individual potentiometer for applying an appropriate voltage to a varactor tuner. Such a memory system is similar to the selective retrieval and memory system of U.S. Pat. No. 3,739,342 to Kortenhaus, dated June 12, 1973, for selectively retrieving articles such as record discs in an automatic photograph. In both instances a binary encoded signal is used to activate an individual memory location to operate or access whatever circuit function or article is associated with the location.
A paper by Sakamoto and Ichinohe, BTR 18, No. 3, August 1972, describes logic circuitry for a 10 key decimal channel number selection system which employs an encoder and an eight bit shift register for converting binary coded channel numbers, through a matrix system, to activate a corresponding potentiometer for tuning. This permits the viewer to input or select a desired channel number, with the shift register acting to store the encoded channel number and supplying a static signal to the switching matrix. To accomodate all-channel tuning, 82 separate potentiometers are necessary.
U.S. Pat. No. 3,748,645 to kawashima July 24, 1973, employs a "dynamic" memory in conjunction with a shift register to provide tuning. Here a pulse train generates the binary codes associated with the locations of the various tuning potentiometers. The channel number codes may be sequentially generated to provide a "sweep" through the FCC allocated set of channel numbers. Separate shift registers are provided for the temporary storage of the generated channel number units and tens digits.
The above-mentioned Tanaka application discloses and claims methods and apparatus for a television tuning system employing a comparator for comparing an asynchronously counted local oscillator frequency (expressed in terms of channel numbers and modular residue corresponding to intrachannel fractions) with encoded input channel number information. A voltage ramp drives the tuner until a condition of equality exists between the derived and desired channel numbers and the modular residue is within predetermined limits. Thus the tuning system responds to a two digit channel number input to tune to a restricted frequency range or "window" about the frequency corresponding to the designated channel number. With this system fine tuning is not required, and programming or set-up of the receiver is unnecessary. The Tanaka tuning system not only provides equal access all-channel tuning but also discloses the channel recall or memory system of this invention. The memory system may be programmed in any desired sequence, to provide sequential tuning among a selected group of channels. The advantage of such a system is readily apparent since the viewer need only operate a single button, or send a single appropriate remote control signal, to change tuning of the receiver to the next preset channel. While the total tuning system including the multi-position memory is fully described in the Tanaka application, this invention is specifically directed to the multi-position memory aspect. As will be seen, the tuning system of this invention also allows the viewer to directly tune to any desired channel without affecting the programmed channels in the memory.